Two classes of compounds are being synthesized (1) triterpenes and (2) indoles andrelated heterocycles. Triterpenoids eonstitute a large group of plant pentacyclic natural products derived from squalene cyclization. We have begun a program to modify two common members of this class, ursolic and oleanolic acid, in a search for novel biological activity. Over the past year, we have synthesized nearly 100 derivatives of these triterpenoids and our results to date indicate four distinct significant biological activities, including cancer chernoprevention and anti-inflammation. Thus, in a structure-activity study, several synthetic triterpenoids reveal a marked inhibition of nitric oxide synthesis (NOS) induced by gamma-interferon or LPS in mouse macrophages. A different set of triterpenoids induces differentiation of HL-60 leukemia cells. In addition, a third sub-group of synthetic triterpenoids has recently been found to be active in suppressing the growth of prostate cancer cells, without cytotoxicity. Finally, some of these novel triterpenoids inhibit cyclooxygenase-2 in a human tumor cell line. For all these new compounds, mass spectrometry is an essential characterization tool.